Optical glass free of thorium



March 5, 1963 w. GEFFCKEN ETAL 3,030,240

OPTICAL GLASS FREE OF THORIUM 2 Sheets-Sheet 1 Filed July 27, 1959 vvv f vvv eo w so 90 3 0 F W A TOW INVENTOR. MAMTA HUL TIC WATER GEFFQKEN a 0 0 4/ a T v 5 10 2O March 5, 1963 w. GEFFCKEN ETAL 1 3,080,240

OPTICAL GLASS FREE OF THORIUM Filed July 27, 1959 2 Sheets-Sheet 2 AAYA PM AAAVA 6O 2 v'vv v 40 mvyvvvm 90 r61 0; 10 20 so so so :0 so so 0 nvvavroRSI WALTER GE PH ENMARQA HULSTICH 3 W A TTOR N E Y5 United States Patent ()fiFice 3,080,240 Patented Mar. 5, 1963 3,080,240 OPTICAL GLASS FREE OF THORIUM Walter Getfcken and Marga Faulstich, Mainz, Germany,

'assignors to Jenaer Glaswcrk Schott & Germ, Mainz,

Germany, a corporation of Germany Filed July 27, 1259, Ser. No. 829,722 Claims priority, application Germany Aug. 26, 1958 5 Claims. (Cl. 106-47) The present invention relates to optical glass compositions which are free of thorium.

Prior to this invention, there has been a disclosure of glass compositions which substantially consist of La O Ta O ZrO and B are free of thorium, and are also intended to contain bivalent oxides and W0 The limits of these known glass compositions in percentages by weight were disclosed to be as follows:

In an example of an optical position of n =l.78, the upper limit of the refraction was given as 11:44.7. However, it may be proved that such a composition in which tent of less than 27% by weight or with an n -value of more than 1.805 can no longer be regarded as stable. A characteristic of these compositions is a certain content of alkaline earth oxide or lithium oxide, and generally of CaO which in all of the examples disclosed is present in amounts of at least 20% of the boric acid content in accordance with a molar ratio of CaO to B 0 of at least 0.216. It is a well known fact that the glass range of pure lanthanum borate, which only exists in the immediate vicinity of the composition La O 60 and is considerably enlarged by such a content in alkaline earths relative to boric acid.

According to the present invention it has been unexpectedly found that a content of bivalent ions or of W0 may be completely avoided, that completely stable glass compositions may be produced merely from B 0 La o and at least 4% by weight of ZrO and/or Ta O and that the optical position of these glass compositions exceeds even the above mentioned types, provided the individual constituents are provided in percentages by weight as follows:

Percent B 0 20 to 40 T3205 0 t0 ZrO 0 to 12 and provided the lanthanum oxide content has an absolute lower limit of 440.04 (ZrO percent by weight and an absolute upper limit of 60% by weight, and that it also lies between narrower limits dependent upon the boric acid and zirconium contents which limits are determined by the values given in the following Table I:

Table I 210;, percent B203 by Wt.

the La O amounts to a maximum of 40% does not result in a usable glass if the BaO and ZnO are omitted or if the W0 does not amount to at least 12%. It is therefore necessary to add bivalent oxides or larger amounts of W0 In order to attain intermediate values, they should be graphically interpolated in the above table. The T3305 content will then lie likewise between two limits which are dependent upon the desired refraction of the glass in accordance with the following Table II:

Table II n ZrOz, percent by wt.

In another prior patent relating to the production of a highly refractive glass, there have also been glass compositions proposed which consist of the oxides of the alkaline earth metals, namely, of La O Ta O ZrO and W0 and therefore correspond in this respect to the above mentioned compositions, but differ therefrom by the requirement that the total of the percentages by weight of La O +Ta O +BaO+ZnO should be greater than 70%, which means that the content in B O +possibly SiO +Al O must be smaller than 30% by weight. Consequently, the refractive indices attained must be higher and extend up to 1.83. A closer examination will show, however, that the glass compositions with a B 0 con- According to the formula given above, in which (ZrO is intended to indicate the percentage of ZIOZ by Weight, the absolute lower limit of the lanthanum oxide content will at 0% of ZrO amount to 44%, while at 5% of ZrO it decreases to 43%, and at 7% of ZrO to 42%. The absolute lower limit of the La O content will decrease to 40% not until the ZrO content amounts to 10%. The existence of such a lower limit is surprising particularly in view of the fact that it could, on the contrary, be assumed that an increase ofthe lanthanum oxide content would result in a decrease in the stability. This is true especially since the prior art as stated in the begining expressly indicated the value 3 of the upperlimit of La 'O to amount to 40% by weight and since it'also restricted the ZrO content to 7% by weight. The glass compositions prepared according to this prior proposal therefore have an La O content The La O contents of the glass compositions according to the invention lie between 40 and 60% by weight and" the Ta O contents amount to to 30% by weight. However, as indicated in FIGURES 2 to 4, the following rewhich lies "below the absolute lower limit. and therefore Strictions pp y require fortheir stabilization a content in bivalent oxides For a ZrO content of 0%, Table IV, lined applies; w or W03,wlrich leads to a considerable impairment of the For aZrO content of 5%', Table IV,11ne 2.appl1es; whilev optical position and, especially if greater amounts of For a ZrO contentof%, Table IV,'hne--3 apphes: W0 are applied, to .a strong yellow discoloration. 7 Intermediate values of ZrO and B 0 are to. be graphi- These. and otherfeatures and. advantages of the present 10 cally interpolated. invention .ascompared with the state of; the prior art will Since La O3=l00-B O ZrO Ta O the La O now be describedin detail with reference to the accomcontents result from the values as indicated and complied panying drawings,,in which--- in Table-I.

Table IV B2051I ZrOz'perceIitL by wt. 40' 37 33.5 30.5 27.5 25.0 22.5 20.0-

calposition of a few known glass compositions anda* few compositions according to the present-invention is entered; while FIGURES 2 to 4 show three-component diagrams in' triangular coordinates of glass compositions according to theinvention.

In FIGURE 1 of the drawings, the optical position of the known glass compositions is indicated by means of small crosses-and that of-the glass compositions according to the invention by means'of small circles.

FIGURES 2w 4 indicate the stable glass range of the four-component systems LagO Ta O ZrO and B 0 as variables, while the zirconium content is shown in each drawing as being constant and amounting in FIGURE 2 to 0%, in FIGURE 3 to.5%, and in FIG- URE 4 to 10%. It should be noticed that at a ZrO content of 0%, the stable glass range does not reach the right-v side limit of the coordinate system. Where the Ta O content amounts to zero. It is therefore impossibleto .pro-. duce stableglass compositions if the contentsof both ZrO and T 21 0 amount to zero. On the contrary, as mentioned in the beginning, such stable compositions require at least a minimum amount of 4% by weight of both ZrO and Ta O taken together.

It may 'be seen from these drawings that, particularly with a ZrO content of 0 to 5%, the range of the other components B 0 La O and T a O forms a very narrow strip, which'means that, with a given amount of boric acid, the admissible La O content can be 'varied only within very small limits. lower limit of 44-004 (ZrO is therefore attainable only in the vicinity of 27% of B O as indicated in FIGURES 2 to 4,-and must be strictly defined, as will be subsequently explained in greated detail. Since at a constant Z1 0 content and a givenarnount of boric acid, the total of La O and Tao, must likewise be constant, since La O +Ta O =100B O ZrO the mentioned re. quirementof a" small variability"applies similarly also t0 121205.

As indicated in FIGURES 2 to 4, the boric acid contents of the glass compositions according to the invention lie between 20 and 40% by weight. The refraction then in efiect depends only upon this B 0 content as indicated with considerable accuracy in the following Table III.

The above mentioned absolute The optical positionof the glass compositions according to the invention-'is-very extreme: This is-true-es'pecially for the area 12 1.75 to 1.80-where very-high-v-val'- ues are attained,- as-well as for refractive indices'above' 1.'825,- asindicated' inFIGURE l inwhich afew'examples are marked by circles. In-thelatter-case'itis not only possible to produce glass compositions with a' refractive in dex of up to 1.87 and more, but these compositions also I have extremely high v-values relative tosuch a refraction, as could previously not be attained without any application of thorium.

The'best optical positions will be attained if theamount of Ta O is held in thevicinity of its'lower limit or, which means practically the same, if the lanthanum oxide content is made at least as high as the mean value resulting from Table 1. Furthermore, the ZrO content should preferably be made as high as possible; for example, up to about 10% forrefractive indices above 1.78.

For refractive indices between 1.74 and 1.78, the upper limit of the zirconium content may be very well expressed by the formula the higher lanthanum oxide contents by a shaded marginal zone in order to indicate that the glass compositions falling within this zone can be obtained without crystalliza- 1 tion only in small units. If the lanthanum. oxide content is reduced by only 1 to 2% and replaced by the same amount of Ta O the stability will increase so quickly that large glass units or batches will become possible. If, however, the lanthanum oxide content is reduced to a value below the lower limit, a partial phase separation will occur.

Provided that pure raw materials are applied, the glass compositions according to the invent-ion will be colorless up to the highest refractive indices, have great hardness, and a very good chemical stability, especially if the Ta O5 contents are not made too small.

For producing the new glass compositions, the purest possible raw materials La O T8205, and ZrO preferably in the form of oxides, and boric 'acid' in the form of boric acid hydrate are intimately mixed with each other and melted in portions in a platinumcrucible at temperatures of 1300 to 1400 C. The highest temperatures will be required for the composition with the highest content in 'ra,o +zpo The refining temperatures should preferably be about 20 higher than the insertion temperatures. The molten mixture is thereafter stirred until it has attained the viscosity necessary for casting, that is, at a temperature between l000 and 1100 C. Finally, the molten mixture is cast in the usual manner into preheated steel molds and then slowly cooled.

The following Table V shows a few examples of the glass compositions according to the invention.

Table V N0. B2 03 LazOa T3205 ZIO: 'nd v 37 55 3 51. 2 37 58 5 52. 1 33 53 14 48. 2 30 53 17 46. 7 25 50 25 43. 4 22 5O 28 41. 7 4O 55 5 1. 747 52. 8 37 53 5 5 1. 754 50. 5 36 58 1 5 1. 757 51. 5 36 59 5 1. 762 50. 5 35 55 5 5 1. 766 49. 8 35 57 3 5 1. 766 50. 3 33 5G 6 5 1. 777 49. 3 30 45 20 5 1. 798 44. 3 30 53 12 5 1. 798 46. 7 28 52 15 5 1. 807 45. 3 23 50 22 5 1. 850 42. 2 20 50 25 5 1. 867 41. 25 50 17 8 1. 840 42. 9 35 50 10 1. 774 48. 3 35 55 10 1. 773 49. 7 34 56 10 1. 781 49. 4 33 52 5 10 1. 787 48. 1 30 5O 10 10 1. 804 46. l 30 55 5 1n 1. 803 47. 2 25 45 20 10 1. 836 42. 8 25 50 1O 1. 837 43. 6 25 51 14 10 1. 841 43. 8 23 48 19 1.0 1. S53 42. 4 21 43 26 10 1. 873 40. O 25 45 18 12 1. 843 42. 5

Although our invention has been illustrated and described with reference to the preferred embodiments thereof, we wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. A thorium oxide free optical glass consisting essentially of, by weight,

3. A thorium oxide free optical glass consisting of the following ingredients in the indicated percentages by weight:

Ingredients Percent by weight B 0 -40 M1 0 40-60 2:0 0-12 T3205 said glass including at lease 4% by weight of one of ZrO Ta O and mixtures thereof.

4. A thorium oxide free optical glass consisting of B 0 La O T a 0 and ZrO the range of percentage by weight of the ingredients in the glass being as follows:

Ingredients- Percent by weight B 0 20-40 1.3.203 Zr0 0-10 T3205 0"3 1 6 in which, when ZrO is present in an amount equal to zero weight percent, the range of percentages by weight of the ingredients in the glass is as follows:

lngredients- Percent by weight B 0 20-37 L21 O 44-58 Ta O 5-3 1 when ZrO is present in an amount equal to 5% by weight the range of percentage by weight of the ingredients in the glass is as follows:

Ingredients Percent by weight B 0 20-37 La O 43-58 Ta O 0-27 and when Z10 is present in an amount equal to 10% by weight the range of percentage by weight of the ingredients in the glass is as follows:

Ingredients- Percent by weight B 0 20-40 La O 40-57 Ta O 0-27 ZIOz=0 B203 LazOa T2205 31 55 s 37 5s a 33 5s 14 so as 17 25 50 25 22 50 2s Zr0g=5 40 55 e7 53 5 36 5s 1 36 59 35 as 5 as 57 a 33 56 e 30 4s 20 a0 53 12 2s 52 15 2a 50 22 20 50 25 ZIOQ=10 as 50 5 as 55 34 56 as 52 a 30 50 10 30 5s 5 25 45 2o 25 50 15 25 51 14. 2a 48 19 21 43 26 ZIOz=12 References Cited in the file of this patent UNITED STATES PATENTS 2,861,000 Geficken et al Nov. 18, 1958 2,866,712 Weissenberg et al Dec. 30, 1958 2,899,322 Bromer et al Aug. 11, 1959 3,006,776 Geficken Oct. 31, 1961 UNITED STATES PATENT OFFICE CERTIFICATE, OF CORRECTION Patent N0o 3 O80 24O March 5,, 1963 I Walter Geffcken et al0 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 29, for "(ZrOg)" read (ZrO line 72 for beginingfl read beg-inning column 3 line 59 for "'greated" read greater column 4, line 12 for "complied" read compiled ---3 column 5, line 65 for "lease" read least Signed and sealed this 1st day of October 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID L-YLADD Attesting Officer 4 Commissioner of Patents 

3. A THORIUM OXIDE FREE OPTICAL GLASS CONSISTING OF THE FOLLOWING INGREDIENTS IN THE INDICATED PERCENTAGES BY WEIGHT: INGREDIENTS PERCENT BY WEIGHT B2O3 20-40 LA2O3 40-60 ZRO2 0-12 TA2O5 0-31 SAID GLASS INCLUDING AT LEASE 4% BY WEIGHT OF ONE OF ZRO2, TA2O5 AND MIXTURES THEROF. 